Power over Ethernet (“PoE”) technology is a system for transmitting electrical power safely, together with data, via an Ethernet cable also known as a local area network (“LAN”) cable. An Institute of Electrical and Electronics Engineers (“IEEE”) standard IEEE 802.3 for PoE requires LAN category 5 cable or higher for high power transmission, but can operate with category 3 LAN cable for transmitting less power. In accordance with the IEEE standard, electrical power is transmitted in common mode over two (2) or more of the differential pairs of wires included in an Ethernet cable from the PSE i.e. either:                1. a power supply included in a PoE-enabled networking device such as an Ethernet switch; or        2. a midspan power supply located somewhere along a length of Ethernet cable.The original IEEE 802.3af-2003 PoE standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA) via an Ethernet cable. The IEEE standard assures delivering only 12.95 W of electrical power at the PD since a length of Ethernet cable dissipates some of the electrical power. The updated IEEE 802.3at-2009 PoE standard, also identified as PoE+ or PoE plus, transmits up to 25.5 W of power via an Ethernet cable. The PoE+ standard prohibits a PD, typically a WiFi access point (AP), a voice-over-IP (VoIP) phone or a security camera, from using all four pairs for power. Despite this prohibition, some PoE products, allegedly compatible with the 802.3at standard, offer up to 51 W of electrical power over a single Ethernet cable by transmitting electrical power via all four (4) of an Ethernet Category 5 cable's differential pairs.        
Some PoE PSE devices send electrical power via otherwise unused conductors in the Ethernet Cable. Such PSE devices are generally termed “passive PoE”. Other PoE PSE devices, commonly known as “active PoE” such as 8-wire 1000BT gigabit PoE, send both electrical power and data to a remote PD via the same Ethernet cable conductors,
The 802.11af standard provides a method whereby the PSE and the PD negotiate the amount of power a PD requires. Using a method specified in the IEEE standard, initially a PoE source transmits a slowly increasing voltage (sawtooth or ramp) to the PD. As the voltage changes, the PD responds by drawing different load currents. The PoE source then “classifies” the PD based on the amount of current the PD draws at each voltage level. For example, a PoE source may assign one PD drawing 15.4 W maximum to one class, and another PD drawing 25.5 W to a different class. Based on the amount of power the PD draws, the PoE source then sets a maximum current level to be supplied to the PD. This process is called “negotiation” and “classification.”
PSE devices that fully implement the IEEE 802.3af or 802.3at PoE standards encounter various technical problems. PSE devices operating in full compliance with the IEEE 802.11af standard work satisfactorily in a typical office environment, but prove unsatisfactory if the PD is outdoors, has multiple splices and/or connectors, or is a long distance from the PoE source. In remote and/or outdoor applications, the Ethernet cable's length often exceeds the initial IEEE standard's 100 meters or 328 feet. The electrical performance of category 5 or 3 Ethernet cable and connectors when used for PoE exhibit unexpected relatively high and unstable electrical resistance between an Ethernet cable's differential pairs of wires, and between those differential pairs and any outer shield. For such installations negotiation and classification in accordance with the IEEE 802.3af standard may fail, particularly during classification for various reasons.                1. Intermittent and resistive connections at the Ethernet cable's terminations frequently when unshielded twisted pair (“UTP”) cables are used outdoors.        2. Short circuits and disconnects can occur, particularly in outdoor applications, most commonly when UTP cable deteriorate, or when the Ethernet cable's termination gets wet, or when the RJ45 connections originally intended for low-current indoor use are used outdoors.        3. Induced electrical noise on conductors carrying electrical power conductors can occur when power is back-fed in a complex network, when PDs include switching regulators, when electrostatic discharge (“ESD”) is encountered (particularly in outdoor situations), and when electromagnetic interference (“EMI”) is inductively, magnetically, and capacitively coupled into the Ethernet cable. For example, an indoor installation in which a long Ethernet cable runs past a series of overhead fluorescent light ballasts.        
Yet another problem is that either or both the PD and the PSE may be damaged by power surges and electrostatic discharge (“ESD”) received via an Ethernet cable or a PSE device's input power connection. PSE devices which fully implement the IEEE 802.3af standard are particularly vulnerable to ESD damage when a field effect transistor (“FET”) is used for switching as recommended by the standard. A FET's low gate-drain breakdown voltage makes them particularly vulnerable to transient electrical surges. A growing use of longer Ethernet cables with outdoor PDs for which UTP cables were not designed creates a network of antennae which attracts large transient electrical surges.
Furthermore, a PD may “lockup” perhaps due to a semiconductor “latchup” in the PD's internal components. A conventional midspan PoE PSE cannot detect if such a latch-up occurs. In many situations, only a complete power-cycling with full shutoff of electrical power supplied by the PSE restore the PD's operation. Conventional PSE's are incapable of automatically detecting and correcting this type of lockup.
Finally, power glitches and brief interruptions of AC power to conventional PSE will cause attached devices to lockup or fail. The most common existing solution to this problem is attach an external uninterruptable power supply (“UPS” thereby providing the PSE with battery backup. A PSE that receives electrical power from an UPS cannot power up multiple PDs in pre-determined sequence with proper delays. Consequently, even though the UPS provides uninterrupted electrical power, if the battery eventually becomes fully discharged when electrical power is subsequently restored the PDs may not operate properly particularly if some PDs must be fully operational before other PDs can begin operation.